This invention relates generally to gas turbine engines and, more particularly to a heat shield for a fuel nozzle.
Fuel nozzles in gas turbine engines provide fuel to a combustion chamber. The nozzles typically transport fuel through a compressor exit flow path. Temperatures around the fuel nozzle at the compressor exit flow path can exceed 1000 degrees Fahrenheit. The high temperatures around the fuel nozzle can cause the fuel passing through an inner passageway of the fuel nozzle to form granules of carbon on the walls of the inner passageway, which is undesirable. In addition, when the temperature of the fuel reaches approximately 300 degrees Fahrenheit, the fuel may begin to vaporize in the inner passageway, thereby resulting in intermittent or non-continuous fuel delivery to the downstream end of the fuel nozzle.
At least some known fuel nozzles include a heat shield which surrounds a nozzle stem of the fuel nozzle and which cooperates with the nozzle stem to define an annular air gap between the heat shield and the nozzle stem. One such known heat shield is described in U.S. Pat. No. 5,269,468, which is assigned to the present assignee. The heat shield and air gap insulate the fuel nozzle from the high temperatures. The heat shield may be attached to the fuel nozzle body by brazing. Low cycle fatigue (LCF) in braze attachments, however, adversely impacts the life of the shield.
A fuel nozzle including a nozzle stem having an annular overhang and a heat shield secured to the overhang is described. More specifically, and in one embodiment, the nozzle stem includes an upstream end and a downstream end. The annular overhang extends from the upstream end of the stem.
The heat shield includes a first end and a second end, and the heat shield is welded to the annular overhang at the heat shield first end. An annular air gap is between the nozzle stem and the heat shield, and the heat shield second end cooperates with the downstream end of the nozzle stem to form an annular opening for permitting air to pass into and out of the air gap.